The sign in the window warned burglars that the homeowner owned a handgun and would use it in self-defense. The state agents knocking on the door were there to confiscate the weapon.

The agents are part of the California Department of Justice’s Armed Prohibited Persons System (APPS), a program that takes firearms from people barred from owning them. The law says that group can include ex-felons and people deemed to be mentally unstable.

Often arriving in SUVs and dressed in black tactical uniforms, the teams regularly sweep through California cities with a list of names and addresses.